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appear to be stable indefinitely. When the solution was buffered with K 2 H P 0 4 ,oxidation to 9, IO-diethyl3,6-phenanthrenediol(6) was negligible, even in samples open to the atmosphere. However, 6 was the only product obtained from photolyses carried out in acidic media.',' Elemental analysis of the yellow crystals was consistent with formula 5. The ir spectrum indicated absence of hydroxyl and presence of highly conjugated carbonyl (1651 cm-l). The electronic absorption in methanol showed A,, mp ( e , ]./mol cm) at 406 (19,600), 287 (23,600), and 221 (8900). The extended unsaturated diketone system of 5 seems without close analogy in the literature; however: adaptation of Woodward's rulesg predicts absorption in the 400-450-mp range, as observed. In addition to characteristic ethyl groups (10 H), the nmr spectrum of 5 showed a doublet pair (4 H ) at 6.1 and 7.6 ppm, assigned to the vinyl protons, and a complex multiplet (6 H) in the 2-3-ppm region, partially obscured by the methylene quartet of the ethyl groups. The mass spectrum obtained by direct inlet at 195" gave a base peak at the parent rnje 268, as well as prominent peaks at rnle 239, 211, 183, and 115 attributable to successive losses of ethyl, ethene, and two carbon monoxide fragments, respectively. Exchange of the active protons cy to the carbonyl groups for deuterium was readily achieved by stirring 5 in NaOCH3--CH30Dat room temperature for 3 hr. The deuterated product exhibited a mass spectrum similar to that of 5 except that most major peaks were shifted higher by 4 n / e units. In addition, loss of 42 rnje units (ketene) from fragments of 5 was replaced by a corresponding decrease of 44 mje units in the spectrum of 5-dJ.I" The 6 H multiplet at 2--3 ppm in the nmr spectrum of 5 became a 2 H singlet at 2.3 ppm in the spectrum of 5 4 , as expected for the now unsplit signal of the 4a and 4b protons. New bands were observed in the ir spectrum at 221 1 and 2131 cni-' (C-D stretch). These results are all in excellent agreement with structure 5. Changes in the uv-visible absorption spectrum of dilute (3 X IO-,; M ) solutions of diethylstilbestrol upon successive short irradiations at 254 m p indicated efficient and virtually quantitative' conversion to 5. The presence of an isosbestic point at 267 nip in these consecutive-spectra diagrams testified to the constant molar relationship between product and reactant and to the absence of either dark or photochemical side reactions. The thermal stability of 5, both toward oxidation to 6 and reversion to 2, was shown by the absence of change in the electronic spectra of photolyzed solutions stored in the dark for several months. On the (7) Isolation of phenol 6 without detection of 5 on photolysis of 2 in acetic acid was reported previously by P. Hugelshofer, J. Kalvoda, and I
